This invention relates, in general, to semiconductor devices, and more particularly, to bipolar transistors and methods of fabrication.
Many high voltage bipolar transistors are vertical devices, wherein a collector electrode is on one surface of a semiconductor substrate and wherein an emitter and a base electrode are on an opposite surface of the semiconductor substrate. The semiconductor substrate typically has a thickness greater than approximately 10 microns in order to provide sufficient physical separation between the collector and the emitter. The large physical separation increases the collector-to-emitter breakdown voltage and enables the vertical bipolar transistor to be used in high voltage applications. However, the large physical separation also increases the collector resistance, which degrades the drive capability and the speed of the vertical bipolar transistor.
Other high voltage bipolar transistors are lateral devices that have collector, emitter, and base contacts on the same side of a semiconductor substrate. However, lateral bipolar transistors typically have long base lengths and high parasitic capacitances between a base region and the underlying semiconductor substrate. As a result of these drawbacks, the speed and the gain of the lateral bipolar transistor is degraded.
Accordingly, a need exists for a bipolar transistor that has small parasitic resistances and capacitances, that is suitable for high speed applications, and that can be integrated into high voltage and high power technologies.